This invention relates generally to emission spectroscopy and more particularly to a method and an apparatus for emission spectroscopic analysis which utilizes spark discharge.
In emission spectroscopic analysis using spark discharge, it is customary to pretreat the surface of a sample to be analyzed by applying spark discharges to the sample surface before analysis is conducted so as to reduce the adverse influence of small scars and/or pinholes on or in the sample surface and/or foreign matters attached thereto on the results of analysis, thereby improving the accuracy of analysis. The pretreatment requires high-energy spark discharges conducted for more than 10 seconds in order to conduct an analysis for 5 seconds. The spark discharges for pretreatment of a sample will be referred to as the "preparatory discharges". The more preparatory discharges are conducted, the higher the accuracy of analysis becomes. After a sufficient number of preparatory discharges have been applied to a sample surface, spark discharges for analysis are applied to the sample surface pretreated by the preparatory discharges. The discharges for analysis will be referred to as the "analytic discharges".
The reason why the time required for preparatory discharges is longer than the time required for analytic discharges is that the position in the surface of a sample which is struck by each of the spark discharges produced in one operation of analysis is uncertain, so that the whole area of the sample surface must be treated beforehand by preparatory discharges. The more accurate an analysis is to be made, the longer period of time the preparatory discharges require.
Accordingly, the primary object of the invention is to provide a method and an apparatus for emission spectroscopy analysis which utilize spark discharge as a light source and which are capable of not only shortening the time required for analysis substantially as compared with the conventional methods and instruments but also materially improving the accuracy of analysis.
The analytic discharge is conducted with high energy, so that it is highly capable of vaporizing a sample. The resulting background light, however, is strong as compared with the emission lines of the component elements of the sample, with resulting decrease in the accuracy off analysis. Therefore, low-energy discharge is suitable for analysis itself.
If the energy for analytic discharge is too low, however, the amount of the sample components vaporized decreases and the intensity of the light of the spectral emission lines produced becomes weak, with resulting reduction of the sensitivity and accuracy of analysis. Therefore, a sufficient amount of the sample must be vaporized by analytic discharges so that there is a limit to which the energy level of the analytic discharges can be lowered, with resulting difficulty in reducing the background light.
Accordingly, another object of the invention is to provide a method and an apparatus for emission spectroscopic analysis which utilize spark discharge as a light source and which are capable of reducing the amount of energy for analytic discharge while simultaneously improving the accuracy and sensitivity of analysis.